*
I believe if you run multiple Romex(NM) cables through conduit it should be derated but can you run multiple cables through the same hole in framing. If I’m running crosswise to the joists can I run multiple cables through the same hole for the length of the house? Any guidelines as to the size of the hole vs. the number or size of conductors allowed before derating? Or is it allowed at all?
TIA,
Jerry
Replies
*
Of course you can!
I have heard the limit is 24" so if your framework is more than 24" thick, you would have to derate it. But you can run Romex through up to 24" of conduit [for protection] without derating.
Make sure your holes are further than 1 1/4" from the edge of the stud or you will have to protect the cable with metal plates.
{I couldn't find any reference to the "24"" in the Code but I didn't look real hard.]
-Peter
*Thanks Peter,I know I've seen it done, ie., two cables of 12/2 through a 3/4" hole in the plate, but when I started thinking of a long (45') parallel run of two 6/3 cables, I started thinking of things like minimum hole size vs. size/number of conductors. I guess as long as the cables aren't bundled and they fit through the holes they shouldn't have to be derated. I just couldn't find anything definitive in the NEC or on the web. Of course, I'll keep physical protection in mind.Jerry
*JerryI did not try to find it in NEC, buyt Code Check say that cables BUNDLED together for more than 2ft are to be derated.The question is what is bunbled. In a case like yours I supsect that it is whatever the inspector says that it is.It would certainly be easy for an inspect to look at that run and call it bundled.
*Bill,So this is gray area, open to local interpetation? Maybe instead of being lazy, I should just drill the extra holes. ;-)Thanks,Jerry
*Jerry, this has all to do about heat, and little else.Should your romex heat up, it should be able to transfer that from the conductor to the cable sheath, and from there to atmosphere.Same standards applied to THHN in conduit, yield theconductors/conduit size ratio.Technically, anything you do to insulate or lessen the heat transfer from a romex conductor would derate the conductor.Most folks will oversize by one diameter just in case.50 foot run for a 15 amp circuit? Run 12 ga. wire for example.Some high Amperage applications actually use a non-conductive fluid to cool the conductors, more by ensuring a superior heat-transfer than by refridgeration.-GWC
*Unless there is some reason to beleive that the wall cavities will be overheated I wouldn't worry too much about it. There are two pieces to the derating system. Temperature and fill. As long as the hole is large enough to resonably pull the romex through without damaging the jacket and the confinement of the hole doesn't go for more than 24" you should be fine on the fill point. Remember that the majority of the romex is surrounded by insulation that slows it ability to lose heat.As for the heat as long as you don't run romex across a hot air duct, a bad practice by any means, or otherwise substantially heat the wire I wouldn't worry too much.It was suggested that oversizing the wires might be a good idea. In extrem cases I agree. Romex in a 12 and 14 gauges are, in a sense, already derated. First, the 20 and 15 Amp ratings from a physics point of veiw as amperage applied per cicular mil of cross section is oversized. Second even though romex is actually composed of wires insulated by 90 degree C (194 dgrees F)insulation and then a jacket it is rated at 60 degrees C(140 degrees F) for the listed ampacity. This compensates for it being buried in insulation and trapped in a wall. Modern romex has been used for quite some time without major problems and assuming it is conscientiously installed according to the code it should safely serve for many many years. On the other hand even the safest system will fail if sloppily installed or misused. Your question is a good one and shows that you are both concerned enough to seek answers and smart enough to know that you dont know. Many get in trouble by guessing or just winging it. In this case I wouldn't worry too much.Be safe. Take care and have a little fun.
*One of my inspectors limits romex run in same holes to 3. He made me redo a run too. That was in Westchester, but here in Warren County, NY, you can do a million things that code says no to and as I see it the local electricians do all that they can get away with. Like running romex stapled over romex and too close to an edge of a stud and running a dozen wires in the main holes run out from the main panel.near the stream wiring to Westchester standards in Warren County,aj
*4lorn and aj,Thanks to both - I spoke to the inspector and he said what 4lorn said almost word for word.>He went further to say anymore than 9 conductors in the same hole would have to be derated (like conduit rules). He was more concerned about neatness and min. 1-1/4" from stud face.aj - it would seem you can run 3 12/3 cables or 4 12/2 and one 12/3 cables in the same hole according to my inspector, but you'd have to make sure that that the hole needed wouldn't be too close to the stud edges (if 2x4 frame). Maybe that's why your inspector only like to see three. I'll probobly only pull two anyway.Jerry